This invention relates generally to methods and apparatus for roadway resurfacing, and more particularly to new and improved asphalt recycling methods and apparatus for rejuvenating old roadway surfaces into new highway pavements. Road resurfacing methods and apparatus such as are set forth in U.S. Pat. Nos. 3,361,042; 4,011,023; 4,103,973 and 4,124,325 provide means for resurfacing asphalt pavement surfaces by some of the most inexpensive and effective processes known to date.
As in most industries however, economic prosperity in the asphalt repaving business depends on continuing improvements in product quality and/or reductions in the cost of the product provided. This is especially true in the repaving business where the large majority of customers are either government agencies or municipalities generally operating under very restrictive fiscal budgets.
Most asphalt road surfaces are made up of a combination of stone, sand, and asphalt cement mixed together in appropriate proportions and under proper conditions. One of the most important mixing conditions is that of heating the asphalt components to temperatures high enough to liquify the asphalt cements and thereby allow them to spread evenly and uniformly bind the asphalt components together. The most comonly used asphalt cements become liquified somewhere around 200 degrees Farenheit, but unfortunately these cements also have relatively low flashpoints, usually around 475 degrees Farenheit. Therefore, the temperature during mixing must be carefully controlled to obtain a high quality product and avoid the danger of fire.
In a modern asphalt production factory, attaining proper conditions or mixing asphalt is not difficult. However, attempting to revitalize an existing roadway surface by mixing asphalt components already in the form of a road pavement proves a much more difficult task. This is large part due to the problems associated with penetrating sufficient amounts of heat into the existing asphalt road surface. For example, heating an upper surface of asphalt road to around 400 degrees Farenheit will create temperatures of about 200 degrees Farenheit approximately 3/4 of an inch down into the asphalt, and only temperatures of around 120 degrees Farenheit at a depth of approximately one inch. Mixing together these various heated levels will produce a material having a fairly uniform temperature of approximately 300 degrees Farenheit, which is the minimum temperature needed to mix a high quality asphalt product. Trying to heat the upper surface much higher in an attempt to affect more than an inch of asphalt will likely set the surface on fire and burn it. Burning the asphalt not only degrades the quality of the end product but also causes air pollution and subjects buildings and foliage adjacent the repaving operations to a danger of being set on fire.
Therefore, using known machinery and methods, it is only possible to effectively revitalize approximately one inch of an existing asphalt roadway surface. Layering new asphalt mix on top of a revitalized inch of road surface, or mixing new hot mix into the revitalized inch without treating the old asphalt surface below, the revitalized inch will not result in a road pavement with quality comparable to that of a brand new asphalt road. Such attempts can also prove expensive and time consuming.